XLV 



REVIEW OF DR. HANNOVER'S MEMOIR: " UEBER 



DIE ENTWICKELUNG UND DEN BAU DES 



SAUGETHIERZAHNS " 



Quart. Journ. Microsc. Set., vol. v., 1857,//. 166-171 



In this beautifully illustrated memoir, Dr. Hannover contributes 

 much interesting information with regard to the histology of the 

 dental tissues in the Mammalia generally ; but we suspect that both 

 by the author, and by the scientific public, the pith of the essay will 

 be considered to lie in the views respecting the development of the 

 teeth, whose exposition occupies so large a portion of it. It is to 

 these, therefore, that we shall chiefly direct the reader's attention in 

 the course of the following critical analysis. Dr. Hannover com- 

 mences his work thus : — 



" The dental sac of Mammalia contains four elements, which, 

 without coalescing, lie in contact, and are distinguishable by their very 

 peculiar structure. Below, on the bottom of the sac and coalesced 

 (verwachsen) with it, lies a soft body, which at a very early period 

 acquires the form of the crown of the tooth. This body is the dentine- 

 germ (dentin-keim) ; by a process which we shall call ' dentification ' 

 it becomes dentine, a substance characterised by the branched tubules 

 which it contains. The dentine-germ is immediately covered by the 

 enamel-germ : this consists of cells (the enamel-cells), on the whole 

 arranged perpendicularly, which are at first very soft, but subsequently, 

 by calcification, become solid columns, and constitute the hardest 

 substance of the tooth — the enamel. Most externally in the dental 

 sac lies the cement-germ, which, by a process of ossification quite 

 analogous to that which takes place in bone, is changed into cement. 



